Inductively heated godets are widely used for guiding or conveying continuous synthetic fiber yarns and the like and are particularly useful in stretching and texturizing devices for the treatment and processing of such yarns. In operation, the yarns are generally wound several times about the outer circumference of the driven outer shell or casing of the godet and heat is thereby conducted to the yarn for the purpose of, for example, plastic deformation or fixation.
Godets of this general type are characterized by an induction coil being mounted in a stationary coaxial position about a laminated magnetic core which is composed of a ferromagnetic material and which is rigidly connected to the frame of the device. A drive shaft extends coaxially through the center of the laminated pack and the rotatable casing which surrounds the induction coil and laminated pack assembly is secured to the end of this drive shaft. An example of such a godet is shown in U.S. Pat. No. 3,487,187 issued Dec. 30, 1969, the disclosure of which is incorporated herein by reference.
One significant problem in these godets has been their inability to function well at high thread treating temperatures on the order of 250.degree. C. together with high yarn speeds. With a thread contact temperature of about 250.degree. C. on the outer casing surface, the temperature in the winding and along the inside of the hollow shell or casing rises to 300.degree. C. or more, and the heat developed internally of the godet causes severe damage to the laminated core pack and especially to the bearings where lubricant may be completely evaporated. Therefore, these high working temperatures have been avoided with inductively heated godets, and correspondingly low thread speeds have been required to achieve a satisfactory thermal treatment.
Another significant problem encountered with such godets, has been the loosening of the induction coil from the iron core of the laminated pack in operation. This problem is caused by the differing coefficients of thermal expansion of the material used for the coil (e.g. tin, aluminum, or copper) and the material used for the laminated pack (e.g. iron). This problem is particularly acute at high operating speeds where the yarn is conveyed at speeds of 4,000 m/min. and more. At such high speeds, slight vibrations created in the godet become significant and may result in an axial shift and wear of the coil.